The specific aims of this proposal are (1) to modify spinal fixation devices (metal struts used internally along with bone grafts in surgery of the spine) so that the forces applied to them can be monitored outside the body, and (2) to determine the time related load sharing capacity of the spinal fusion mass. The device will be tested in sheep in preparation for using them in humans. The information derived will be used to prevent failures (20 percent we now see when spinal fixation devices are used to treat fracture dislocation of the spine (with or without spinal cord injury) and failures seen when these devices are used to treat scoliosis and the collapising spine. We have already done preliminary work on micro-instrumentation of the fixation device at the Rehabilitation Engineering Research and Development Center of the Palo Alto Veterans Administration Medical Center. Development of advanced microcircuitry over the last five years by the Center for Integrated Electronics in Medicine at Stanford has made available a small telemetry package which can be modified to interface with the fixation device and be completely contained within the body. We are in a unique position to utilize this advanced technology to obtain, for the first time, quantitative data over a six month period of the forces applied to the spinal fixation device and the fusion mass after spinal surgery. All mechanical data will be supported by roentgenographic, histological and biochemical analyses to provide a composite of the variables influencing spinal column repair. Our team of rehabilitation engineers, spinal cord injury physicians and orthopedic surgeons have been working together for the last five years on problems related to vertebral stabilization in spinal cord injury patients. This proposal is a continuation of our efforts in this area.